Go back on some lines (7)
I believe the answer is:
reverse
'go back' is the definition.
(I've seen this before)
'on some lines' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'some lines' becomes 'verse' (I've seen this before**).
're'+'verse'='REVERSE'
(Other definitions for reverse that I've seen before include "Britannia's place" , "Upset" , "Move backwards" , "Turn inside out or upside down" , "contrary" .)